The present invention relates to a one-piece compression-molded, substantially cylindrical plug for plugging a sleeve wrapped up of paper or cardboard.
Plugs of the type under discussion are substantially cylindrical hollow elements pressed or molded of the mixture of fibers with a heat-hardenable binder and utilized for wrapped sleeves of paper or cardboard. Such a plug is cylindrical over the half of its length and has a substantially the same outer diameter over that half while its other half or remaining portion is conical. Thickenings are provided on the peripheral face of the plug.
Such a plug has been disclosed, for example, in "Compression molded plug for rolled sleeves," Fa. Werzalit AG & Co., Unternehmenbereich Industrieproducte, 7141 Oberstenfeld.
Known plugs of the foregoing type are utilized with rolled sleeves which are preferably made of paper, cardboard and/or paperboard according to German standard No. DIN6748. After the wrapping material is wrapped about the sleeve the wrapped up roll is removed from the wrapping device and the plug is driven into such roll before the latter is transported to a packing device.
End faces of such rolls or sleeves wrapped with wrapping material are covered firstly with circular discs or washers, for example of paperboard by a packing device, and then the periphery of the roll of wrapping material is wound up with paper in the packing machine. The circular discs or washers are secured to the plugs by means of clamps.
When tolerances of the external diameter of the plug and/or internal diameter of the wrapped-up sleeve are added to negative values it can occur that the plug, during fastening of the circular disc by a required large driving force for the clamps, is driven into the sleeve over a predetermined length.
This, however, causes a disadvantageous effect which resides in that the disc does not snugly abut the end face of the wrapped up sleeve but the disc becomes at its outer edge concavely deformed. This leads to the fact that the deformed edge of the disc is not detected in the packing device in which wrapping up of the rolls is carried out automatically, and the packing can be incorrect.